Micro arc is a local and instantaneous abnormal discharge in a plasma. The micro arc is generated in a plasma processing apparatus. As the plasma processing apparatus, a capacity-coupling type plasma processing apparatus by parallel plate electrodes such as shown in FIG. 5 is given as an example. In this plasma processing apparatus, parallel plate electrodes 20 are provided in a processing chamber 10, and a substrate W is placed in a grounded lower electrode (anode) 20a. A high frequency power source 40 is connected to an upper electrode (cathode) 20b through a matching unit 30, and a high frequency electric power is applied between the electrodes 20. When a reactive gas is supplied to the processing chamber 10, arc discharge occurs between the electrodes 20, and a plasma P is generated. By the plasma P, the reactive gas is activated and a processing such as a film forming is applied on the substrate W.
During arc discharge, dust falls from the electrodes 20, or a thin film is peeled off from the surfaces of the electrodes 20. The fallen dust and the peeled thin film trigger the micro arc to be generated. A damage caused by the micro arc is generated not only on the side of the cathode 20b, where abnormality is easily caused on the surface of an electrode, but also on the surface of the substrate on the anode 20a or on an inner wall of a processing chamber. In FIG. 5, micro arcs 50a, 50b, and 50c generated on the surface of the substrate, on the surface of the cathode, and on the inner wall of the processing chamber are respectively shown. An electrode cover (not shown) formed by joining a plurality of ceramics plates is used around the substrate W, and in some cases, the micro arc is generated also in its joint. Note that the substrate W is a glass substrate for LCD, and a semiconductor wafer substrate or the like.